Is Find Maximum Number of String Pairs easy or hard?

Find Maximum Number of String Pairs is categorized as an Easy problem. The main concept is recognizing reversed string pairs and using a hash table to avoid unnecessary comparisons, which makes the optimized solution straightforward.

Find Maximum Number of String Pairs Python/Java solution

In Python, you typically use a set to track seen strings and check for reversed matches in O(1) average time. In Java, the same logic is implemented using a HashSet or HashMap. Both implementations follow the same algorithm: reverse the string, check for existence, and update the pair count.

How to solve Find Maximum Number of String Pairs in O(n)?

Iterate through the array once and maintain a hash set of seen strings. For each string, generate its reversed version and check if it already exists in the set. If found, increment the pair count and remove the matched string; otherwise, insert the current string. This ensures each string participates in at most one pair.

What is the best approach for Find Maximum Number of String Pairs?

The most efficient approach uses a hash map or hash set to store previously seen strings. For each word, compute its reversed string and check if that reversed version already exists in the hash structure. This reduces the search from comparing every pair to a constant‑time lookup, giving O(n) time complexity and O(n) space complexity.

Is Find Maximum Number of String Pairs asked at Google/Amazon/Meta?

Problems involving hash maps and reverse string matching appear frequently in interviews at companies like Amazon, Google, and Meta. While this exact question may vary, the underlying pattern of using hash tables for quick complement lookups is common in coding interviews.

What data structure is used in Find Maximum Number of String Pairs?

The optimal solution uses a hash table structure such as a HashSet or HashMap. It enables constant‑time average lookup to check whether the reverse of a string has already been encountered while iterating through the array.

What is the time complexity of Find Maximum Number of String Pairs?

The brute force approach runs in O(n^2) time because every string is compared with every other string. The optimized hash table solution runs in O(n) time since each string is processed once and reverse lookups occur in constant time on average.

Description Hints 2 Solution Video 0:12

2744. Find Maximum Number of String Pairs

Easy82.4% acceptance

You are given a 0-indexed array words consisting of distinct strings.

The string words[i] can be paired with the string words[j] if:

The string words[i] is equal to the reversed string of words[j].
0 <= i < j < words.length.

Return the maximum number of pairs that can be formed from the array words.

Note that each string can belong in at most one pair.

Example 1:

Input: words = ["cd","ac","dc","ca","zz"]
Output: 2
Explanation: In this example, we can form 2 pair of strings in the following way:
- We pair the 0^th string with the 2^nd string, as the reversed string of word[0] is "dc" and is equal to words[2].
- We pair the 1^st string with the 3^rd string, as the reversed string of word[1] is "ca" and is equal to words[3].
It can be proven that 2 is the maximum number of pairs that can be formed.

Example 2:

Input: words = ["ab","ba","cc"]
Output: 1
Explanation: In this example, we can form 1 pair of strings in the following way:
- We pair the 0^th string with the 1^st string, as the reversed string of words[1] is "ab" and is equal to words[0].
It can be proven that 1 is the maximum number of pairs that can be formed.

Example 3:

Input: words = ["aa","ab"]
Output: 0
Explanation: In this example, we are unable to form any pair of strings.

Constraints:

1 <= words.length <= 50
words[i].length == 2
words consists of distinct strings.
words[i] contains only lowercase English letters.

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Hint 1

Notice that array words consist of distinct strings.

Hint 2

Iterate over all indices (i, j) and check if they can be paired.

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2744. Find Maximum Number of String Pairs

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